Reproductive activity, morphology, physiology and antigenicity of Trypanosoma lewisi and other rodent trypanosomes is altered during infection by an antibody, ablastin, synthesized by the host. This laboratory has characterized some of these alterations and antibody responses of infected hosts. Current objectives are to determine the mechanism of the ablastic effect and the role of the antibody in regulation of the parasitemia. The hypothesis is that ablastin interacts with its eliciting antigens (ablastinogen) on surface mebranes and affects transport processes of the parasites. The research involves; ablastin and ablastinogen purification and characterization and studies on alterations in membranes and transport processes. Ablastin characterization includes the production of antisera in infected and immunized animals, purification of gamma-globulins from sera, separations of ablastin from other trypanosome specific Ig and "normal" globulins by immunospecific adsorption and assays of reproduction inhibition in vitro. Homogeneity will be characterized by acrylamide electrophoresis and immunologically. Ablastinogen characterization requires quantities of trypanosomes and/or the isolation of antigen from plasma of immunosuppressed animals, in vivo, in vitro assays of ablastin responses after immunization with washed triturated trypanosomes or plasma from infected animals, separations of ablastinogen in immunospecific adsorption or isokinetic density gradients and ion exchange or gel filtration chromatography. Homogeneity of the preparations will be established by chromatography, electrophoresis and immunodiffusion. Thermal and pH stability and solvent effects on the antigen will be determined, and its carbohydrate, lipid and protein composition. DEAE charomatography coupled with particle sizing of trypanosomes will indicate charge-size relationships and effects of ablastin on surface charges. Membrane conformation and structural alterations will be characterized by electron paramagnetic resonance measurements on incorporated spin-labeled cholesterol and fatty acids. Protein coat alterations may be visualized with ferritin and peroxidase labeled globulins of normal or immune animals. Membrane and surface changes will be compared with kinetic data on transport inhibition of C14-alpha-methyl-D-glucose by ablastin.